Java's StringBuilder

StringBuilder

Actually, stringbuilder can contain an array inside it as such:

public String convert(String s, int numRows) {
    int index=0;
    StringBuilder[] st= new StringBuilder[numRows];
    for(int i =0;i<st.length;i++){
        st[i] = new StringBuilder();
    }
    while(index < s.length()){
        for(int i=0;i<numRows && index <s.length();i++){
            st[i].append(s.charAt(index++));
        }
        for(int i=numRows-2; i>0 && index<s.length();i--){
            st[i].append(s.charAt(index++));
        }
        
    }
    StringBuilder result = new StringBuilder();
    for(int i=0;i<st.length;i++){
        result.append(st[i]);
    }
    return result.toString();
}

setCharAt()

sb.setCharAt(i,’’) where you can place something at a certain index You can’t put an empty literal like (‘’) so when you set it with certain pattern, use replaceAll() to put empty (“”) like .replaceAll(“\+”,””)